It is an urgent issue to establish a technique for enabling recycling of tools and mechanical parts coated with inorganic materials such as poly-crystalline diamond (which may be hereinafter abbreviated as “PCD”) through the de-coating.
This is now described by taking tools such as a drill and an end mill which are each formed of tool steel or cemented carbide as examples. Each of the tools uses tool steel or cemented carbide coated with TiN, TiAlN, DLC, or PCD.
With the use of the tools, these coatings wear out or peel off to cause the tools to reach the end of their service life. Such used tools have conventionally been discarded but recycling through the de-coating and further repetition of coating has been desired. It has been required to perform efficient and uniform de-coating and not to cause damage to substrates.
Methods of plasma or ion irradiation in a vacuum have already been put into practical use as proposals for such a de-coating method (see, for example, Non-Patent Literatures 1 and 2).
However, the former plasma irradiation method is low in de-coating efficiency because plasma forms, on the front surface of a substrate, a space electrical layer called a sheath where no ion collision occurs, thus forming a barrier that may hinder a de-coating action (see Non-Patent Literature 3).
Further, the latter ion irradiation method may lead to insufficient de-coating or cause thin film residue through re-evaporation on the remaining coating as a result of sputtering of a substrate.
In addition, there is also a case where a tool having a thin film of TiAlN or the like is subjected to de-coating using a chemical agent heated to a high temperature but this case has a problem in terms of use of an environmentally unfriendly chemical agent.